1. Field of the Invention
The invention relates to a method and an apparatus for producing a thin glass ribbon, and relates to a thin glass ribbon produced according to such method. The thin glass ribbon may even be a glass film.
2. Description of Related Art
Thin glass is increasingly employed for various applications, such as in the sectors of consumer electronics, for example as cover glasses for semiconductor modules, for organic LED light sources, or for thin or curved display devices, or in sectors of renewable energy or energy technology, such as in solar cells. Examples include touch panels, capacitors, thin film batteries, flexible circuit boards, flexible OLEDs, flexible photovoltaic modules, and even e-papers. Thin glass is getting more and more into the focus for many applications due to its excellent properties such as chemical resistance, thermal shock resistance, and heat resistance, gas tightness, its high electrical insulation capability, matched expansion coefficients, flexibility, high optical quality, and light transmission, as well as high surface quality with very low roughness in case of a fire-polished surface of the two thin glass faces.
Processes for producing a thin glass ribbon in which the thin glass ribbon is drawn from a molten glass in a thickness of less than or equal to 300 micrometers, usually cause thickenings, referred to as borders, that are formed at the two lateral edges across the moving or drawing direction of the thin glass ribbon that is being drawn, as compared to the thinner useful glass in the center of the thin glass ribbon. These borders usually have a thickness of about 350 μm to 400 μm.
In order to be capable to coil or bend a thin glass in form of a glass ribbon even to rather small diameters so as to save volume space and in particular with regard to a compact storage and cost-effective transportation to further processing locations, it is advantageous or necessary to separate these borders. Furthermore it is desirable to separate the borders since they may lead to stresses in the glass caused by uneven cooling of the entire glass ribbon, and may therefore be problematic. Hitherto, the severing of the borders has usually been effected in the cold post-processing section on the annealed molten glass. As a severing or cutting method for the thin glass, conventional technologies are employed, such as separating by scoring using wheels and subsequent breaking, as well as light-optical methods, such as by laser scribing and subsequent breaking.
For example, WO 2010/099304 A2 also discloses a method for separating a portion from a glass ribbon at a predetermined separation line. In this case, the glass ribbon is first shaped in a region along the separation line, at a viscosity of less than or equal to 7×1014 poises (dPa·s), by causing the region to be at a temperature at or above the softening point, in particular by means of a laser, plasma, microwave, flame, or a focused infrared beam, and by transversely applying a load to the glass ribbon so as to form a constricted section having a thickness that is less than the thickness of the glass ribbon on each side of the region. Subsequently, the glass ribbon shaped in this way is cooled so as to have a viscosity of greater than 7×1014 poises (dPa·s). Then, a tension is applied to the cooled glass ribbon so that the glass ribbon breaks along the constricted section and thus is separated along the predefined separation line.
However, due to the broken edges with associated roughness and microcracks, such separation processes may lead to an uncontrolled breakage of the glass.
Therefore, in order to prevent cracks and breakage from arising in particular in the coiled or bent glass ribbon, the quality and integrity of the edges is of particular importance.
Furthermore, a particular problem with the drawing of thin glasses is the fact that due to the considerably larger glass thickness the border cools much more slowly than the useful glass between the border regions. The slower cooling causes the glass in the border regions to become more compressed than in the center thereby creating stresses in the glass ribbon which may lead to warpage.